Hello,
what is the reason for the change:
[...]
There is already a test for C11 some lines above:
#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
/* Do nothing. They are language keywords. */
#else
/* Not supported. Implement them using our versions. */
If you want C11 in GCC, you have to specify -std=c11 or -std=gnu11.